I am getting my Metra 65 overbored and they asked me what the piston/cylinder wall clearance should be. They guy said he could estimate for me, but it would be much better if I knew the exact numbers.
I am getting my Metra 65 overbored and they asked me what the piston/cylinder wall clearance should be. They guy said he could estimate for me, but it would be much better if I knew the exact numbers.
till the piston slides threw .. thats what i would say.
usually when i over bore i do it by half millimeters and i just do it till the piston drops threw with out force .
Anybody know numbers though?
I believe .002 inches to .003 inches. Stock pistons in an iron bore were between .001 and .002 inches, so .002 inches would be a safe bet.
Thanks man. I thought that there must be some kind of standard for similar cylinders.
Has anyone whose done this/ gotten it done? Please chime in if so... the guys at the machine shop were skeptical this was right.
I got a metra overbored but I dont have the numbers at the moment.
do you have the old piston?
if so bring it to your dudes and have them measure it and the cylinder bore. Then you have your clearance.
I am going to go with .0001-.0002.. maybe 3-4... Ed
This is the response I just got from Metrakit themselves
Hello Max
I would recommend a .0022 or .056mm clearance. Thanks for using Metrakit I
hope this is helpful please feel free to email me with any other questions
you might have.
Louie Peverini
Metrakit USA
So .002 was a good guess. (Just in MM not inches).
.002 is a good FINAL clearance after honing for most piston fits, but requires break-in. Racing types will need to go .003 to .004 for instant RPM's. You have to allow for proper honing and utilize the new piston for your measurement, not a used one.
I usually hone the last thousand or two till I get the proper fit. When fitted properly, a dry piston slipped in a dry cylinder on a nice, flat bench will WHOOSH as it glides through when released. I call this the PUSSY fit!
Sorry for offending anybody that may bat for the other team...I won't go there for them.
Seasoned Motor Builder's Trick for free!!
Micrormeters (inside & outside) are the tool of choice for acquiring this sensitive of a fit. But after doing hundreds, I've come to be able to "feel" it by slipping a long .0015 or .002 feeler gauge in with the piston along the center of a skirt. (Note: don't force it or you're too tight) You should be able to draw the feeler gauge out with the slightest bit of resistance w/o carrying the piston with it.
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